If electrical short-circuit occurs inside a battery with high energy density such as a lithium ion battery, abnormal heat generation is caused depending on the structure, and an accident such as a burn, a fire or the like can occur.
Thus, in a battery with high energy density such as a lithium ion battery, such a test is conducted that the battery is punctured by a nail made of metal so as to destroy an insulating bulkhead inside and to cause internal short-circuit and to check that heat generation or ignition resulting in the accident does not occur. This test is called a nail puncture test.